PRODUCER Beth Polson, an Emmy-laden veteran of 20 years' experience with all three major networks, can't forget the conversation she had last February.

''I was pitching movie-of-the-week ideas to a top network exec when he said, 'Give me [a movie like] last Monday's,' '' she recalls. Thumbing quickly through the TV Guide on her desk, she found the description of a techno-suspense-thriller that was panned by critics but reached a respectable 26 million households.

Ms. Polson tells the story to indicate how the ratings-at-all-costs environment has engulfed network entertainment television as never before. Threatened from all sides -- by multichannel cable, satellite-delivery systems, syndicators, pre-recorded videos, and even computer applications -- the once-mighty ABC, CBS, and NBC are scrambling to hold audiences just as a revolution in the delivery of home entertainment bears down on them.

The panic to hold viewers is the motive behind what many feel -- and content analysts confirm -- are network programs containing more sexual explicitness, more violence, and cruder language. Because cable TV is not held to the standards that govern public-owned airwaves, cable programs can push the boundaries of taste and propriety without censorship -- and win viewers in the process.

''We can point to the explosion of cable in more daring handling of sexual material, nudity, and language by the conventional networks,'' says Garth Jowett, a University of Houston professor and author of several books on TV.

While ratings have always been important, the current ''be watched or perish'' concern with numbers is turning the world of television upside down, say producers, writers, and directors.

''What is happening is so sad,'' Polson says. ''This is the largest tool of communication, and what contribution are we making?''

Grant Tinker, one of television's most experienced and respected producers and the former chairman of NBC, describes the challenges posed by today's accelerating competition, soaring costs, and corporate-investor mentality that favors quick profits over creativity and quality.

''If I arrived on the television production scene now and tried to start MTM [Mary Tyler Moore Productions], I couldn't do it,'' Mr. Tinker says. (MTM produced some of TV's top programs, including ''The Mary Tyler Moore Show,'' ''Lou Grant,'' ''Hill St. Blues,'' and others.) The reasons: TV producers now must please wealthy backers, since networks no longer cover production costs, and network programmers insist that shows succeed almost immediately, rather than allowing for audiences to build. This takes a toll on creativity, Tinker says.

PARADOXICALLY, the hypercompetitive environment has had a secondary, positive effect. If panic and pressure are producing tons of dross, they also have created a fistful of jewels.

''Television is better now than it has ever been,'' says Howard Rosenberg, Pulitzer Prize-winning TV critic for the Los Angeles Times, who also teaches television history at the University of Southern California. He mentions such shows as ''Seinfeld,'' ''Frasier,'' ''The Larry Sanders Show,'' ''NYPD Blue,'' ''Homicide,'' ''Ellen,'' and others. One has to be selective, he cautions. ''Who made up this rule that television is supposed to divert us for seven hours a day?'' he says. ''Part of our complaint about TV as a wasteland is our own fault for not being selective enough.''

''Television is moving in both directions at the same time,'' says Brian Stonehill, a media theorist at Pomona (Calif.) College. ''On one side, they are learning to bring us such greatly packaged and aesthetically serious extravaganzas as 'The Three Tenors' or Alvin Ailey dancers. At the same time, there is more sludge, drivel, and pablum than ever before, following the money to be made by titillation. That makes it harder for uplifting themes to compete.''

At the close of the 1994-95 network prime-time season last month, there was more bad news for the major networks: Despite a wave of creative hits in recent seasons, the big three's share of viewers continues to slip. Prime-time ratings for ABC, CBS, and NBC fell from 37.4 percent last season to 34.6 percent today. In 1980, 53.3 percent of all homes with televisions were tuned to the networks during prime time.

GOOD or bad, entertainment television is headed for a second 50 years altogether different from the first 50. Norman Lear -- for 40 years a producer of hits that included the 1970s smash series, ''All in the Family'' -- calls the mid-1990s ''the third birth of television.'' First, coast-to-coast live broadcasts began in 1950; the advent of cable and cable networks (HBO, Showtime, CNN) followed 20 years later. Now, as Vice President Al Gore and a host of others admonish us, we are at the advent of digital, interactive television and the information superhighway.

But until consumers are up to speed with new ways of accessing and processing video and other information in their homes -- through television and personal computers -- most industry-watchers say television entertainment programming will stumble along in its current incarnation.

''We are still in the early stages of multichannel television,'' says Chris Dixon, a media analyst with the brokerage firm Paine Webber. ''Until the average Joe is comfortable with downloading entertainment into his house through electronic devices, you're going to see the same diet of Oprah, Roseanne, and [Rush] Limbaugh.''

Times are changing, though, says Al Burton, producer and developer of such shows as ''One Day at a Time,'' ''The Jeffersons,'' and ''Square Pegs.'' He says there is a meaner spirit in television entertainment today.

Noting the success of such new dramas as ''ER,'' and ''NYPD Blue,'' he says, ''Unless you have major skepticism and cynicism in your main character, you are not perceived to be as smart as the producer whose show does have it.'' The pressures for producers to reach out to a broader universe of viewers also means targeting new ethnic groups and cultures, he adds, including those that may not have the same command of English, history, and academic interest as previous audiences.

With the exception of such shows as ''Frasier,'' he says, ''writers are shying away from high-cultural references and allowing less- cultured uses of the English language.''

Reaching out to the broadest universe of viewers also means leaving smaller audiences behind. Because of advertisers' increased interest in 18-to-49-year-old consumers, for instance, shows for older viewers have been dropped in recent years. Even a ratings and critical success like CBS's ''Burke's Law,'' which was beating ABC and NBC in its time slot, was canceled because programmers didn't want viewers to think their Friday-evening lineup was tilting to ''oldsters.''

Perhaps the largest indicator of network television's change in content, many say, is the 8-9 p.m. ''family viewing hour.'' As programming guidelines have loosened and the definition of what is appropriate for early evening is broadened, the proliferation of sexually suggestive material and portrayals of issues once thought too sophisticated for younger audiences has accelerated.

In the 1970s, the time slot was peppered with such innocent shows as ''The Waltons,'' ''The Brady Bunch,'' ''The Partridge Family,'' ''Happy Days,'' and ''Little House on the Prairie.'' In the 1980s, the relatively simple and pure was still the order of the day: ''Webster,'' ''Facts of Life,'' ''The Bill Cosby Show,'' ''Full House.''

But a take a look at the time-slot this season: Fox TV's ''Melrose Place,'' a nighttime soap about babes and hunks lusting after power and each another; ''Martin,'' in which the lead becomes involved in sexually suggestive situations; and ''Roseanne,'' which deals with many provocative subjects. Programs in the 9 p.m. slot include even more controversial adult issues.

''It's clear a new environment exists for what's OK in family-viewing prime time,'' Tinker says. ''Networks more and more seem to be doing whatever they want.''

This has not met with broad acquiescence. Parents and young people, in studies and polls, express dissatisfaction with values portrayed on TV, and critics such as Michael Medved warn that the entertainment industry risks alienating its audience.

Others argue that taste and artistic quality are not necessarily the same thing. Mainstream morals may be offended at the same time good or even great programs are produced. A prime example from TV history is CBS's ''All in the Family.'' The show focused on the myopic attitudes of a loud-mouthed bigot while becoming one of the most critically acclaimed series of all time.

Likewise for this year's ''NYPD Blue,'' say several critics. Using prime time's first-ever disclaimer for partial nudity, adult language, and violence, the show pushes the content envelope while winning kudos for depictions of character, dialogue, and crime situations.

Professor Jowett goes further. Pointing to high-caliber series such as ''ER,'' ''Ellen,'' ''Friends,'' ''Mad About You,'' and ''Frasier,'' he says, ''If I were looking for quality acting and scriptwriting consistency, I would look to TV rather than movies these days.''

Waylon Green, co-executive producer of ''NYPD Blue,'' says top writers have moved back to television from theater and movies. Writers can hone their dialogue, description, and plots over several episodes or a season. A TV movie can stretch to a miniseries of up to four, two-hour episodes. That allows lots of creative elbow room compared with a two-hour movie-theater release.

''You can get a lot more information into television, and play things out in natural, dramatic order,'' Mr. Green says. ''If you try some of those things in movies, you are usually dead.'' Other benefits: seeing your work quickly, more often, and sometimes unedited.

Another reason critics say writing has improved on some shows is sheer necessity. Without the big budgets for high-concept, high-tech gadgetry that drive the scripts of their movie cousins, TV writers have to better craft their dialogue, characters, and plots.

Whatever choices viewers are exercising at the moment, in three to five years they will have so many viewing choices that a three-, four-, or six-network era may seem a quaint memory. ''Because of digital storage and delivery systems, viewers will be able to summon, watch, interact with, and store as many program types and broadcasting niches as they can imagine,'' says media theorist Stonehill. One system, TeleTV -- video on demand via phone lines -- was announced this month.

In the end, the power to shape the content and character of television in the future rests with the viewer, critics and other observers say. ''Driven by its ratings, TV must be a follower of the public will even as it shapes that will,'' Stonehill says. ''It is not a malevolent force. It is a fragile and unstable mirror that reflects what is both silly and sublime about us.''

''My wish for television as we stand at this threshold,'' producer Lear says, ''is for it to recover a sense of constructive engagement with American culture and politics. My wish is for a new birth of socially visionary leadership....

''[New technologies] will not necessarily help bring us together as a nation, heal the wounds of our cynical society, or help educate today's young people. Such needs have little to do with technology -- and everything to do with the character, values, and aspirations that we will bring to the shaping of that technology.''